Re: DINOSAUR digest 3384

[Jorge Dichenberg <jorgedich@yahoo.com>]

--- K and T Dykes <ktdykes@arcor.de> wrote:

> <<I would first ask some meteorologist/astronomer.
> How would real atmosphere react? Would falling
> microscopic ejecta indeed deliver single heat
> pulse?>>
> 
> Remarkably or otherwise, one author is based at the
> Program in Atmospheric and Oceanic Sciences and
> Laboratory for Atmospheric and Space Physics at the
> University of Colorado.  He seems to agree with the
> conclusions in the paper.

He does not discuss above. 

> <<They themselves say that thermal radiation was
> "except
> where Earth surface was shielded by very thick cloud
> cover". In the scale of Earth, hundreds of thousands
> of km2 are covered by thick clouds every day.>>
> 
> They say thick cloud would've provided some cover,
> in that fuel wouldn't be ignited (p.762).  Fires
> aren't the killing mechanism they're proposing. 
> They don't say it would've kept out the thermal
> radiatio

I think this means that. Heat needed to kill large
animals would also dry surrounding vegetation and
start a fire (actually fire would burst first, due to
heat capacity of big animal). 

And reverse - if heat radiation is blocked by clouds
to the point not to ignite vegetation, it would also
not "broil alive" animals.

(thermal radiation = heat emanating from atmosphere).

> I think the quotation is a bit wrong, Jerzy, as they
> don't quite say that.  Page 764 contains: "No
> evidence has been offered that late Maastrichtian
> pterosaurs or nonavian dinosaurs could burrow, swim,
> or dive (Padian, 1983)."

Mercy for them. Late Maastrichtian ones are unlikely
to differ in this from earlier dinosaurs - which could
wade in water and swim.

> <<They fail to explain selective extinction. They
> propose that all Cretaceous mammals were burrowers
> or entered water. No evidence of that, especially
> together with suggestion that no small or young
> non-avian dinosaurs behaved similarily.>>
> 
> They certainly address selective extinction, as
> that's rather the point they're making.  In order to
> survive, you needed protection either from water or
> soil.  They don't propose all Cretaceous mammals
> were burrowers or swimmers.  Rather, the ones who
> survived may well have been.  The evidence offered
> is that burrowing is a widespread mammalian
> lifestyle, and some modern mammals show semi-aquatic
> careers are also viable.  Therefore, it's not
> unreasonable to assume that some, (not all),
> Maastrichtian mammals lived similarly

Shortly - absence of proof is proof of absence? 

For KT surviving mammals there is no proof that they
could all (or most) burrow and swim, but they grant
them this possibility. For dinosaurs which were more
diverse, they claim that lack of proof mean that they
all could not burrow or swim. 

> <<They cannot explain why birds survived, which
> mostly don't shelter - including ratites, numerous
> waterbirds, shorebirds etc.>>
> 
> A lot of water birds are capable of diving, and they
> definitely do mention that.  

Yes - they mention their feathers would have been
burned as soon as resurfaced. 

They also mention many
> lineages of birds contain burrowers.  They
> furthermore explicitely address ratites and point
> out, that the earliest forms (presently known from
> the Paleocene) are relatively small.  

Yes - they list avian lineages surviving KT and duly
say that many DON'T contain any burrowers. 

In most of remaining clades, burrowing is restricted
to few derived taxa so likely evolved recently. This
applies to eg. ratites (kiwi).

Nitpicking, on top of this they lump hole nesting with
burrowing. In this case, tree hole is no protection
from heat radiation enough to ignite a whole tree. 

> As the paper wasn't discussing fire as a killing
> mechanism, any vulnerability to smoke is of no
> relevance.  

Above - heat radiation enough to kill big animals
would also start fires. Air pollution would favor
largest animals over smaller.
 
> <<They state that dinosaur eggs and young would
> survive. They propose obligatory parental care in
> all non-avian dinosaurs - no evidence of that.>>
> 
> I thought they provided evidence by discussing the
> almost universal parental care found among living
> dinosaurs.  For example, (page 764): "Even large,
> precocial hatchlings in modern birds (a dinosaurian
> subset) almost always require care after they leave
> the nest."  They could also have added parental care
> among crocodiles, but they presumably deliberately
> limited themselves to dinosaurs for this point. 
> While not being necessarily conclusive, Jerzy,
> that's certainly evidence.

Parental care among crocodilians and some birds is
that juveniles become independent when very small. For
dinosaurs it would mean that young would survive
together with mammals and birds. 

Never in dinosaur literature I found suggestion that
in all diverse groups in Late Cretaceous, young were
dependent from parents until reaching giant size. 

(just again hole - they transplant parental habits
from small subgroup of dinosaurs to all. But they were
unwilling to transplant burrowing or swimming habits
in the same way).

> I think that's being too short, Jerzy, as they
> addressed rather a lot of the points, which you
> stated they didn't address.

I thought I write far too long already. Thanks for
reminding.

Jerzy



                
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